I have a Deere 160LC excavator that has a pressurized hydraulic tank. The manual shows how to release the pressure when doing something with the hydraulic tank, however, it doesn't say what kinda of pressure is in there or how it gets there since there are no instructions about repressurizing it. And for that matter why is it pressurized, I thought the hydraulic return was to atmospheric pressure. I'm assuming it's a low pressure and due to heating of the oil, but that's a dangerous assumption. Anyone know?
The tanks is pressurized to help feed pumps and keep the oil from foaming. Pressure is usually under 3bar. To repressurize I usually just start machine and raise idle slightly, let sit running for about ten minutes.
The pressure is usually around 15 PSI and is obtained by the raising and lowering of the level in the tank when you pick up the boom and stick and then lower them. There is a vent valve on the tank that will let air in when the level goes down but will not let it back out when the level goes back up. Older machines used a radiator type cap which is cheap but they are prone to loosing their seal over time. Most people don't think about the air in the tank until after they take a hose loose somewhere and can't stop the oil.
A significant amount of your pressure rise in a pressurized tank comes from thermal expansion. As the oil is warmed by machine use, the oil expands. The breather valve (usually but not always) located at the filter regulates the maximum pressure in the tank. It also should breathe air into the tank if the pressure suddenly drops due to oil level falling due to normal hydraulic operation or sudden oil loss
Exactly! Well put.
I learned the hard way you want to vent that tank before opening the oil fill port. All i wanted to do top off the oil level, I covered the whole machine with oil, dumped about 2 pails on the ground, and showered twice!
On this same machine how do you take the cap of the hydraulic tank off? The manual and the cap says to use a 4mm allen key. When sliding the key into the slot it goes all the way through the hole. In fact we tried using all different sizes of allen keys to unlock the cap, but we can't get the locking pin to release. Is there any way to get the cap off? We were thinking about "forcing it" but that will break the cap. The other way is to take the entire stem out.
The hex key will go all the way through the hole, from side to side. When you turn the hex key, it retracts a small locking pin that prevents cap removal without hex key. Many folks don't know this and will attempt to remove cap, sometimes with force, thereby bending the locking pin to where it will no longer retract. You may just have to remove the entire cap assembly by removing allen bolts that mount it to tank.
you put the allen wrench in and twist. While you still have the allen wrench twisted, then you twist the cap off. All the allen wrench does is move a little locking pin when you twist it so you can twist the cap off. Be careful When taking the cap off It will blow most of the oil out if it is still pressurized. I usually twist the cap and tip it over to release the pressure just do it slowly.
The hex key does not engage any locking pin. We have tried several other different sizes of allen keys and none of them engage any pin. It looks like the mechanism has been knocked out. The locking pin sticks out a little bit from the housing, we have also tried using a pair of pliers and pulling on the locking pin, but it doesn't move. By the schematic it looks like if I can get the cap off I can remove 2 bolts to remove the entire cap assemble (to replace it), but I have to get the cap off first.